Fault-Tolerant Method to Reduce Voltage Stress of Submodules in Postfault Condition for Regenerative MMC-Based Drive

In this article, we propose a fault-tolerant strategy to recover the full performance of a modular multilevel converter (MMC) under submodule (SM) fault condition for regenerative medium-voltage drive applications. The proposed method has the feature to retrieve line voltage amplitude during the postfault condition back to its nominal value. In this method, the missing capacity of the converter due to the fault condition is compensated by all remaining healthy SMs. The main advantage of the proposed method in comparison with previous works is that it imposes a lower voltage stress on switches in postfault conditions without severe circulating current. Remaining healthy SMs also operate at a similar condition, which leads to the feature of homogeneous distribution of loss and temperature in all parts of the converter. The proposed method is applicable for the regenerative MMC-based drives as well as the back-to-back configuration of MMC without adding cost or complexity to the whole system. A generalized approach is presented and its result is compared with other methods. The simulation and experimental results are provided to validate the performance and feasibility of the proposed method that can effectively enhance the fault-tolerant capability of this converter.